The spark arcs to ground on the first plug, not the second.
The first plug is pos polarity and the second plug is reverse polarity...which is why the electode wears faster on the first than on the second. If the spark arced to ground on BOTH plugs, they would have to be wired in Parallel, not Series. And they would then both have the SAME polarity.
But they don't b/c it is a series circuit.


The coils secondary winding has a Pos and a Neg tower. The bottom tower one [ TA+ ..that goes directly on the plug ] is the pos terminal. The other one [ TB-] is the neg terminal and has the return plug wire from the second plug .
The flow goes from pos TA+ to the first plug, arcs to ground, from ground to the second plug, arcs back to the center electrode, and completes the SERIES circuit back to the neg side of the coils TB- secondary winding. A closed / completed circuit, using the two plugs in series. That is the complete secondary loop..completely isolated form any other circuit/s.
You can get a code for the first misfire with a bad wire on the second b/c the first plug can't fire with a bad plug wire to complete the circuit.
Each plug fires to complete the series circuit, but the one under no load/compression [ Waste Spark] only needs 2-3 K to jump...and these coils have a 40K output to overcome that and still get enough ramp to work the EVENT plug. The coils output is dependent on what is needed , and that is
what is monitored on the primary winding trigger amp draw.
So, to say both plugs fire to ground is not correct on a Series Waste Spark system, which simply means that the plugs are out of phase, polarity wise with each other b/c it is a series circuit. And being a series circuit, the flow has to return to the neg terminal of the coil thru the 2 plug gaps.
One an EVENT firing, and the other a Wasted firing, with the combined load on the coil being the total of both plugs series circuit.
Which was CTH point to begin with.....

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A Dalton